I have been reading for a while today and am more confused than ever. I have an existing attached garage that is just stud walls now. The exterior of the wall is just plywood/fiberboard covered by siding. I am on a real budget so I was going to just throw in some R-13 kraft faced insulation and some 5/8" drywall over that. My question is how do I put a vapor barrier between the fiberglass/exterior side of the insulation and the exterior wall of the garage. In new construction I would think this would be covered by Tyvek or similar but I can't do that. What do I put on the existing walls to keep them vapor sealed or don't I have to worry about it and just stick the faced insulation (faced side in) and be done with it?

Good question.... interested to see what people suggest I have similar issue too.

i have never put vapor barrier on the exterior wall. we have always just put up the insulation and then put the vapor barrier over the insulation, then the drywall. you can also buy insulation with a vapor barrier already built in. it cost a little more then the normal insulation but saves you the time and effort of putting up the vapor barrier.

like this
http://1.bp.blogspot.com/_kAAcqUbxlFE/SVmVSY8kWdI/AAAAAAAAAd0/sZtLGmCq6Ao/s400/NewVaporShield.jpg

i know i bought this stuff once at lowes when i did my garage. here is a link to the brand
http://www.jmhomeowner.com/products/product.asp?category=FiberGlass&Product=ComfortTherm

Then if you use the insulation with the backing on it in the case of the Home Depot products it is "Kraft" faced do you need an additional vapor barrier?

This stuff
http://www.homedepot.com/Building-Materials-Insulation-Fiberglass-Rolls/h_d1/N-5yc1vZ1xkkZbay7/R-100317775/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

The vapor barrier goes on the warm side of the insulation. In Milwaukee, where you heat the room more than you cool it, the vapor barrier is inside the insulation. Floridians place the vapor barrier on the outer side of the insulation.
Kraft barrier is barely OK as a barrier. Get the unfaced fiberglas and a 6mil? VB and tape all of the seams.

Products like Tyvek aren't intended for use as a vapor barrier. They are there to help reduce air intrusion from the outside. Vapor barriers always go to the side that has conditioned air. A vapor barrier on the exterior side would trap moisture in an area where it can't easily escape, promoting mold growth.

Even if you do use kraft faced insulation, go with the plastic on top of it and tape the seams.

Looks like I have my answer. You guys rock. Now to figure out what to do in the attic area. More reading is on the way!

faced insulation like the r-13 you refer to has the vapor barrier on it,thats what the paper is.usually unfaced you use plastic